1. Field of the Invention
The invention relates to a data transmission method and a network element such as a base station controller in a telecommunication system, the system utilizing frequency hopping.
2. Description of the Related Art
Frequency hopping consists of changing the frequency used by a channel at regular intervals. Frequency hopping is used to attenuate the influence of attenuation due to, for instance, Rayleigh fading. One advance achieved is interferer diversity: in high traffic areas the capacity of a cellular system is limited by its own interference caused by frequency reuse. The carrier-to-interference ratio may vary considerably between calls. The carrier level changes with the mobile station position relative to the base station, with the number of obstacles between them, etc. The interference level changes depending on whether the frequency is being used by another call in a nearby cell, and it also varies according to the distance to the interfering source, its level, etc. With frequency hopping, it is possible to circulate channels between users and thus shorten the time each user has a connection of poor quality.
Typically, in cellular networks, when frequency hopping is used, the interference is most considerable in the areas, where several cells having similar frequency hopping lists (MA list, mobile allocation frequency list) and different random hopping sequences are bordering each other. Another problem is due to the fact that cellular networks usually consist of multiple separate cell clusters. The interference is usually highest in the proximity of cell border areas where there are cells belonging to different cell clusters.